Transportation systems that use a transmission to drive a carriage along a track system are well known particularly when the track system used is some form of suspended cable arrangement.
Most prior art cable systems, however, employ a movable cable that is looped about rotating wheels at each end to provide propulsion to a car or other transport means mounted on an associated fixed cable. Such systems require great lengths of cable and the moving cable is prone to sagging. These systems are also limited to straight line motion between the rotating wheels and any turns in the system have to occur at cable support towers. With existing systems, there is a tendency for the transport means to be pulled off the cable whenever a turn is encountered. As a result, these prior art transmission systems are not designed to negotiate corners. As well, many of the systems where the load is drawn along the support cable by a movable cable are limited in their ability to move up a steep gradient. Prior art clamping systems have been developed that clamp and hold the cable in order to move up a steep incline, however, these systems cause undue cable and clamp wear.
U.S. Pat. No. 3,406,833 to Read discloses a skyline conveying device for harvesting timber composed of individual hoisting units suspended from the skyline. A very long endless drive cable driven by a remote engine is used to move the hoisting units.
U.S. Pat. No. 2,601,228 to Sheilds discloses a hoist system using a cable suspended between two masts. This system also uses an endless drive cable driven by a remote engine. As in the patent to Read, these long endless drive cables are subject to wear and are time consuming to install as a pulley system must be set up to handle the endless cable.
U.S. Pat. No. 1,313,358 to Watkins discloses a tractor for aerial ropeways comprising a travelling carriage with its own power supply. The embodiment of FIG. 8 of this patent shows a endless belt with friction elements for engaging and moving along the aerial ropeway. The friction elements rely on the weight of the device and suspended load to ensure secure engagement with the ropeway and there is a tendency for the device of Watkins to slip.
U.S. Pat. Nos. 404,499 and 404,500 to Pendelton discloses a gripping device for cable railways that uses an endless belt with gripping elements to grasp a moving cable in order to accelerate the car to which the gripping device is attached to the speed of the cable.
U.S. Pat. No. 3,448,694 to Seyfried teaches a cable gripping device for suspended cable cars that is capable of running along a stationary cable as with present invention. Seyfried employs a relatively crude clamping system for holding and gripping the stationary cable and therefore is very prone to slippage on the cable.
Further examples of prior art cable transmission systems are shown in U.S. Pat. No. 2,132,558 to Braune and U.S. Pat. No. 828,645 to Fouts.
In addition, all the prior art patents discussed above are limited to travelling along essentially straight lengths of cable. They are unable to negotiate tight curves in the cable system on which they move.
Some of the devices of the prior art also suffer from the disadvantage that they employ gripping means for holding the cable or rope way along which they move that bear the entire weight of a transmission and any suspended load. The result is that the cable or rope way is always subject to wear even if there is no slippage of the transmission. If slippage does occur, wear of the cable or rope is even more pronounced.